The Popillia japonica, commonly known as the Japanese beetle, poses an increasing threat to agriculture and gardens in Europe, particularly in France, where it may soon establish itself. This insect, native to Asia, is classified as a priority quarantine organism by the European Union due to its devastating economic and environmental impacts. Indeed, it attacks over 300 plant species, ranging from agricultural crops to ornamental plants. Let’s learn more about this potential (and yet another) threat!
How to Recognise the Japanese Beetle?
The Japanese beetle measures about 10 to 12 mm in length. Its small size can lead to confusion with other beetles found in France. However, it is distinguished by its metallic green head and thorax, its copper-brown elytra, and the five tufts of white bristles located on the sides of its abdomen, along with two more at the end of it.
Finally, the Japanese beetle is smaller than other common European beetles. Its body shape is compact and slightly rounded, with short, segmented antennae that end in club-like tips. These antennae are often retracted when it is resting but can be visible when it is moving or feeding.
Life Cycle of the Popillia japonica
The life cycle of the Popillia japonica, or Japanese beetle, is annual and consists of four stages: egg, larva, pupa, and adult. Females lay their eggs in the soil during summer, from which the larvae emerge after about two weeks and feed on plant roots, causing damage until autumn. They then hibernate deep in the soil until spring, where they pupate and transform into adults. Adults are present in summer, feeding on leaves and flowers, before reproducing, thus completing the cycle.
What is its Impact on Plants?
This insect is polyphagous, meaning it feeds on multiple plant species (about 300 species). Adults feed on foliage, flowers, and fruits, leaving the leaves in a skeletal state after their passage. The larvae, on the other hand, cause damage by feeding on the roots of plants, particularly grasses like lawns. Among the most affected plants are grapevines, fruit trees, roses, and many other ornamental and agricultural plants.
In Italy, where the Japanese beetle has been present since 2014, vineyards are particularly vulnerable. The beetles devour grape leaves, thereby reducing the leaf area necessary for photosynthesis and thus for grape ripening. Corn and soybean crops are also severely affected by the Japanese beetle.
Roses are among the most affected ornamental plants. Japanese beetles devour the leaves and flowers, which can lead to complete defoliation. The larvae of the Japanese beetle, which feed on the roots of grasses, also pose a serious problem for lawns.
Obviously, like all invasive species, the Popillia japonica seriously threatens local biodiversity by competing with native beetles for food resources and disrupting natural ecosystems.
Estimation of Agricultural Yield Loss Costs
Precise figures regarding the economic impacts of the Japanese beetle in Europe are still being evaluated, due to the recent introduction of the insect to the continent. However, American experience provides insight into the potential extent of the damage. In the United States, direct and indirect costs (yield losses, treatments, management) related to the Japanese beetle exceed $450 million per year.
With the continued expansion of the Japanese beetle in Europe, economic impacts are expected to increase, particularly if the insect manages to establish itself in France, one of the main wine and agricultural crop-producing countries in Europe. Early prevention and control are therefore essential to minimise damage.
Additionally, there are costs associated with control measures, including expenses for installing pheromone traps, purchasing chemical or biological products, and mobilising teams to monitor and treat infested areas.
Spread of the Popillia japonica
The Japanese beetle is nicknamed "the hitchhiker" due to its ability to travel long distances by clinging to various supports, such as plants, pots, objects, and even modes of transport (trucks, trains, cars, planes). This facilitates its rapid expansion across different territories. Since its introduction in Italy in 2014 and in Switzerland in 2017, the Japanese beetle has seen its population increase, with new outbreaks detected regularly, including in Zurich and Basel in 2023 and 2024.
Coming Soon to France?
Although the Japanese beetle has not yet been detected in France, it is crucial to remain vigilant. In the event of suspected detection, it is recommended to capture the insect (if possible alive) and report it immediately to the Regional Directorate for Food, Agriculture and Forestry (DRAAF). Early reporting will allow for the implementation of appropriate control measures to prevent its establishment in the territory.
Proposed Control Measures and Awareness
In Italy, where the Popillia japonica has been present since 2014, rigorous monitoring and trapping measures have been implemented, including the use of pheromone traps to capture adults and limit their spread. Switzerland, facing the invasion since 2017, has adopted a similar strategy, intensifying monitoring in border areas and using biological control methods, such as introducing nematodes to target larvae in the soil.
The fight against the establishment of the Popillia japonica in France relies on early detection and rapid eradication of initial outbreaks. State services have set up traps equipped with mixed lures (sexual pheromones and floral attractants) along French borders and in strategic areas such as ports and airports. If the insect is detected, an infested area is then delineated and will be subject to enhanced monitoring using a combination of biological, physical, and, as a last resort, chemical methods.
However, everyone can contribute to limiting the spread of this insect by remaining vigilant when purchasing plants or during plant exchanges, as well as by regularly monitoring the plants in their garden.
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